This invention relates to an aircraft environmental control system, and more particularly to an aircraft environmental control system having two separate air cycle machine refrigeration packs, and having the ability to provide independent temperature control for each of the passenger and crew compartments on the aircraft in the event of a failure or inoperability of one pack and the resulting single-pack operation.
An aircraft environmental control system ("ECS") is used to cool, filter, dehumidify, pressurize and otherwise condition the air supplied to both the crew (a.k.a., cockpit, flight deck) and passenger (a.k.a., cabin) compartments. The ECS typically utilizes a source of hot compressed air, such as bleed air from the turbine engine compressor section (during aircraft flight with the engine operating), the auxiliary power unit ("APU") (during ground operation), or both. The hot pressurized bleed air is then typically expanded and cooled in an air cycle machine ("ACM") and associated heat exchangers to provide a cool air supply to the crew and passenger compartments.
On an aircraft having two or more turbine engines, it is known to utilize a first refrigeration system or "pack" for providing the air supply to the crew compartment, and a second, identical refrigeration pack for providing the air supply to the passenger compartment. The two dedicated packs typically operate independently of each other in controlling, inter alia, the temperature of the air supply fed to the associated compartment. Usually, separate and independent temperature controllers are provided for controlling the temperature of the air supplied to the crew and passenger compartments, respectively.
A problem arises, however, in such environmental control systems when there is an operational failure or a forced shut down of either pack. The single pack left operating still supplies air to the associated compartment. However, the single operational pack is now the only supply of air to the compartment associated with the failed pack. For example, upon failure of the flight deck pack, the cabin pack supplies air to both the crew and passenger compartments. However, the temperature of the air supplied to the crew compartment is determined solely by the temperature controller for the passenger compartment. Therefore, the air supplied to the flight deck may not be of a desired temperature. This is sometimes problematic because often the crew and passenger compartments are operated at different temperatures, primarily owing to the different volumes of each compartment and the contents thereof. For example, the crew compartment often contains sophisticated electronic circuitry that requires climate control. On the other hand, the passenger compartment contains a greater number of human passengers.
Heretofore, no known twin-pack environmental control system has been developed that allows the temperature of both compartments to be independently controlled in the event of failure or shut down of one of the packs without adding additional control systems.
Accordingly, it is a primary object of the present invention to provide an aircraft environmental control system that normally provides a pair of independently-operated refrigeration packs, one dedicated to the crew compartment and the other dedicated to the passenger compartment, but provides for independent temperature control of both the crew and passenger compartments during failure of one pack and resulting single-pack operation.
The above and other objects and advantages of the present invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.